A fluid dynamic bearing device is a bearing device which rotatably supports a shaft member through an oil film formed in bearing gaps. The fluid dynamic bearing device has characteristics such as high-speed rotation operation, high rotational accuracy, and quietness. In recent years, by taking advantage of those characteristics, the fluid dynamic bearing device is suitably used as a bearing device for a motor to be mounted to various electrical apparatuses such as information equipment. Specifically, as a bearing device for a motor, the fluid dynamic bearing device may be suitably used in the following: a spindle motor for an information apparatus such as a magnetic disk drive such as an HDD, an optical disk drive for a CD-ROM, CD-R/RW, DVD-ROM/RAM, or the like, or a magneto-optical disk drive for an MD, MO, or the like; a polygon scanner motor of a laser beam printer (LBP); a color wheel motor of a projector; or a fan motor.
For example, a fluid dynamic bearing device for a spindle motor includes a bearing sleeve, and a shaft member inserted along an inner periphery of the bearing sleeve and rotated relative to the bearing sleeve. As the shaft member used in many cases, there may be given one having a flange portion provided at one end of a shaft portion. In this case, radial bearing gaps are formed between an outer peripheral surface of the shaft portion and an inner peripheral surface of the bearing sleeve, and a thrust bearing gap is formed between at least one of end surfaces of the flange portion and a surface opposed thereto (end surface of the bearing sleeve, for example). As types of the shaft member with a flange, there may be given an integration type in which the shaft portion and the flange portion are formed integrally with each other by machine processing such as cutting and a separation type in which the shaft portion and the flange portion are individually manufactured and integrated with each other by an appropriate means.
In the integration type of the shaft member with a flange, although high fastening strength can be secured between the shaft portion and the flange portion, dedicated processing facilities is required for manufacturing the shaft member with a flange, which leads to a remarkable increase in cost. Thus, in recent years, the shaft member with a flange is formed in a separation type in some cases.
As the separation type of the shaft member with a flange, there are well-known various ones. Among those, as a structure in which high fastening strength can be secured between the shaft portion and the flange portion, there is well-known one in which the shaft portion and the flange portion are integrated with each other by welding as disclosed, for example, in JP 3774080 B (Patent Document 1). Further, JP 2004-340368 A (Patent Document 2) discloses a structure in which the shaft member and the flange portion are integrated with each other by welding, specifically, by resistance welding.
Patent Document 1: JP 3774080 B
Patent Document 2: JP 2004-340368 A